Power takeoff devices (hereinafter referred to as "PTOs") are well known throughout industry for their ability to transfer the power of a rotating gear of an engine (herein broadly referred to as a transmission) to which the PTO is attached, to an auxiliary function which performs useful work.
Perhaps the most prominent use for PTOs is on heavy duty trucks equipped with a hydraulic fluid pump for operating various auxiliary functions (i.e. equipment) ancillary to the truck's principal function as a transportation vehicle. Such auxiliary functions characteristically include, for example, hydraulically raising and lowering a dump bed through operation of an underbody dump hoist or the performing of high horsepower operations such as bulk powder dispensing by high speed blowers, hydraulic refuse compacting, winching and the like. In such applications, the PTO is characteristically connected to an appropriate gear of the transmission of the truck which selectively or constantly rotates when the engine is turned on. The PTO, having an output shaft which is then rotated by the transmission gear, generates the necessary horsepower to operate the hydraulic pump which then powers the auxiliary function at its designed workload (horsepower) requirement.
It is, of course, understood, in this respect, that not all PTOs are used on or in association with vehicles. Generally speaking, PTOs of the type contemplated by this invention are envisioned for use in association with any engine, movable or unmovable (vehicular or non-vehicular) having a gear which rotates with engine operation (selectively or constantly) and which may be connected (selectively or constantly) to a PTO according to this invention for rotating the PTO's output shaft. Thus when used herein, the term "transmission" includes not only vehicle drive transmissions, but any engine having a gear rotated by engine operation and capable of having a PTO according to this invention attached to it. Examples of such non-vehicular applications include engines which operate oil rigs, non-vehicular garbage compactors, and non-vehicular winches or bulk blowers.
Often conflicting, from a design perspective, with the need for high horsepower requirements in order to properly perform the auxiliary work required (e.g. bulk powder blowing, etc.), is the envelope of compliance allowed by the truck or engine generically at the location on and around its transmission to which the PTO must be secured. In short, there are simply times and applications when and where a PTO of the necessary size to provide the required horsepower does not fit.
In U.S. Pat. No. 5,542,306 there is disclosed a very advantageous and successful PTO particularly useful in the heavy duty trucking industry. This PTO includes an internally located clutch arrangement for engaging and disengaging the output shaft of the PTO from the transmission of the vehicle, along with an internally located drag brake assembly for preventing inadvertent rotation of the PTO's output shaft caused by clutch plate stickage, etc.
While highly advantageous for most usages, it has been found that for high horsepower applications, e.g. 60 hp or greater as measured at 1000 rpm (output shaft speed) generally equal to or exceeding about 300 lbs. ft., the clutch shift mechanism and drag brake of the PTO of this prior '306 patent must be designed to be of such a size that the resulting PTO is too large to fit into certain important smaller envelopes of compliance experienced in industry within which the PTO must fit. In this respect, of course, it would also be an advantage of any new shift mechanism if it could insure against inadvertent rotation of the PTO's output shaft while, at the same time, eliminating the need for a drag brake mechanism to perform this function, thus avoiding the expense, space, and maintenance time associated with such a drag brake assembly regardless of its size.
A particularly pronounced problem, in this respect, exists in the heavy duty tanker truck bulk blower (e.g. cement powder, sugar, etc.) art. In such usages there is normally experienced a need to provide particularly high horsepower requirements (e.g. typically 60 hp or more @ 1000 rpm), and yet the space (envelope of compliance) adjacent the PTO "window" on many truck chassis all too often does not permit use of a, heretofore, adequately sized PTO of the otherwise highly advantageous type found in the aforesaid '306 patent.
The reason for this size problem arises from the nature of gears, in general, and their relationship to the characteristic of horsepower. In this respect, horsepower is generally defined by the equation: ##EQU1## wherein T is torque, k is a constant (generally recognized as the quantity 5252), Hp is horsepower and rpm is the desired revolutions per minute of the output shaft of the PTO. Hp, of course, is characteristically specified according to the work requirement necessary to perform the auxiliary function (e.g. dispensing powder from the vehicle's tanker body, etc.).
As can be seen, if the envelope for size compliance in a vehicle (or an engine generically) regarding the attachment of a PTO to its transmission is relatively small, the need for the PTO to be of compact design will often conflict with the need to achieve high horsepower. This spacing requirement is exacerbated, for example, if, as in the aforesaid '306 patent, a clutch mechanism and drag brake are employed because, as can be seen from the above equation, when horsepower is increased, so is torque and/or rpm, thus necessitating a larger clutch and drag brake to accommodate the higher horsepower requirement. This, then, enlarges the PTO.
This spacing limitation is further exacerbated if, as in the past, the ultimate shifting mechanism for engaging the PTO with the relevant transmission gear resides, in large part, outside of the housing of the PTO, such as through a shifter cable control or external air shift controls, etc.
While the PTO of the aforesaid U.S. Pat. No. 5,542,306 solved this latter problem by including portions of the shifter mechanism internally, its internal shifting mechanism, as aforesaid, included a clutch plate assembly and a drag brake. When designed to handle high horsepower requirements, e.g. above about 60 hp @ 1000 rpm, the size of the clutch, together with the size of the other components, including the drag brake, have been found to increase the overall size of the ultimate PTO, despite locating a portion of the shift mechanism internally, so as to be too bulky to accommodate various useful envelopes of compliance, particularly on certain heavy duty trucks.
It is, therefore, apparent that there exists a need in the art for a PTO that can accommodate a wide variety of envelopes of compliance and, at the same time, produce sufficient horsepower to accomplish the auxiliary work required, while assuring against inadvertent rotation of the PTO's output shaft without the need for a drag brake assembly. It is, therefore, a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.